linux-kernel - RE: [PATCH] ARM: OMAP: AM33XX: CAN: d_can: Add support for Bosch D

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Date:	Tue, 3 Apr 2012 15:58:22 +0000
From:	"AnilKumar, Chimata" <anilkumar@...com>
To:	Marc Kleine-Budde <mkl@...gutronix.de>
CC:	Wolfgang Grandegger <wg@...ndegger.com>,
	"socketcan@...tkopp.net" <socketcan@...tkopp.net>,
	"m.kleine-budde@...gutronix.de" <m.kleine-budde@...gutronix.de>,
	"linux-can@...r.kernel.org" <linux-can@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Gole, Anant" <anantgole@...com>, "Nori, Sekhar" <nsekhar@...com>
Subject: RE: [PATCH] ARM: OMAP: AM33XX: CAN: d_can: Add support for Bosch
 D_CAN controller

On Tue, Apr 03, 2012 at 21:03:40, Marc Kleine-Budde wrote:
> On 04/03/2012 04:29 PM, AnilKumar, Chimata wrote:
> >>>> Please explain why this CAN controller cannot be handled by the existing
> >>>> C_CAN driver, eventually with some extensions. The register layout seems
> >>>> almost identical, at least.
> >>>>
> >>>> Wolfgang.
> >>>>
> >>>
> >>> These are the some of the pointers I can say, why I had gone for separate
> >>> file instead of existing driver:
> >>> * In case of D_CAN driver we can see all the registers are 32bit length
> >>>   but in case of C_CAN registers are in 16bit length.
> >>
> >> How many bits in these 32 bit registers are used?
> > 
> > In some cases (D_CAN_TXRQ, D_CAN_INTPND, D_CAN_MSGVAL) I have used all the
> > bits, in some cases used few bits.
> > 
> > Roughly I can say that its (higher 16bits) % of usages is similar as compare
> > to 16bits 
> > 
> > While checking the status of TXRequest registers and INT pending register,
> > which is a hot code path, we have to put if checks for register access.
> 
> The c_can already has a c_can_read_reg32() function. It's for example
> used in the rx_poll function. You can make it a function pointer (i.e.
> pric->read_reg32()) for easy abstraction.

This won't fit for D_CAN case because offsets are different in c_can compared
to d_can. For example if I read CONTROL_REG register (0x0) in case of d_can,
which will read only control register. In case of c_can it will read
CONTROL_REG + STATUS register values in single read

> 
> >>> * Some of the registers, bit masks are different, so we have to add
> >>>   checks on every API for differentiating the kind of device
> >>
> >> Which registers are this? Can you give us an example?
> > 
> > I am pointing out some of the resisters
> > * Single registers in case of D_CAN but multiple register in case of C_CAN
> >   So masks will change MASK, ARB, INTPND
> > * D_CAN_IFCMD is the combination of COMM request and COMM mask registers
> 
> Maybe you can use the read_reg32 function on both c_can and d_can.

Above comment applies here as well

> 
> regards, Marc
> 
> -- 
> Pengutronix e.K.                  | Marc Kleine-Budde           |
> Industrial Linux Solutions        | Phone: +49-231-2826-924     |
> Vertretung West/Dortmund          | Fax:   +49-5121-206917-5555 |
> Amtsgericht Hildesheim, HRA 2686  | http://www.pengutronix.de   |
> 
> 

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